U.S. Pat. No. 6,523,450 discloses an add-on armor in the form of a multi-layer panel adapted for the external attachment to the bottom of a helicopter at a distance 2″ therefrom. The panel comprises an inner layer made of ceramic material, an outer layer, which may be polyurethane, and a middle layer therebetween which is in contact with both inner and outer layer and which may be of aramid polyamide.
U.S. Pat. No. 4,398,446 discloses different add-on armor arrangements designed for the attachment to a side wall of a military vehicle to provide different levels of ballistic protection. The difference in the arrangements is mainly in the number of armor layers and their location relative to the vehicle's side wall. In particular, in some arrangements where only one armor layer is used, it is mounted either directly or close to the vehicle's side wall or at a location spaced therefrom by spacers, whilst in the arrangements where two armor layers are used, one of them is mounted directly or close to the vehicle's side wall and the other—at a location spaced therefrom. In all the cases, each armor layer is comprised of tiles whose edges abut each other to define a substantially uninterrupted armor surface. The material from which the tiles are made may be any conventional structural materials with anti-ballistic properties, such as a composite ceramic material.
U.S. Pat. No. 5,221,807 discloses a ballistic armor with front and rear layers, which are spaced from each other by a spacing layer. The front layer is made of a ceramic material formed with blind holes, and it is designed to score impacting projectiles before they strike the rear layer, which functions as a main armor layer. The rear, main armor layer may be in the form of a two-layer plate in which one of the layers is made of sintered ceramic and the other layer is made of Kevlar™, ceramic matrix composite or steel.